1. Field of the Invention
The present invention relates to a wireless IC device, particularly to a wireless IC device preferably for use in an RFID (Radio Frequency Identification) system.
2. Description of the Related Art
In recent years, as an article information management system, an RFID system that has been in practical use performs non-contact communication using an electromagnetic field and transmits predetermined information between a reader-writer which generates an induced magnetic field and an RFID tag attached to an article. This RFID tag includes a wireless IC chip which stores predetermined information and processes a predetermined high-frequency signal and an antenna (radiator) which transmits and receives a high-frequency signal.
The RFID system is in some cases used in information management of a printed wiring board included in various electronic devices. As this type of printed wiring board, those described in Japanese Unexamined Patent Application Publication No. 11-515094 and Japanese Unexamined Patent Application Publication No. 2009-153166 are known.
In the printed wiring board described in Japanese Unexamined Patent Application Publication No. 11-515094, an RFID element which processes a radio signal is mounted on a surface of a multilayer substrate, and an antenna pattern serving as a radiating element is formed on the surface and in internal layers. In this printed wiring board, the size of the antenna pattern needs to be increased to improve the gain of the antenna. The increase in size of the antenna pattern, however, causes an increase in size of the printed wiring board itself.
Meanwhile, the printed wiring board described in Japanese Unexamined Patent Application Publication No. 2009-153166 uses a loop-shaped electrode to cause an electrode functioning as a ground of the printed wiring board to also function as a radiating element. It is therefore possible to improve the gain without causing an increase in size of the printed wiring board. Generally, however, various mounted components, such as a semiconductor IC chip and a chip capacitor, are mounted on a surface layer of the printed wiring board. Due to the influence of these mounted components, therefore, particularly a radiation gain toward the surface layer fails to be sufficiently obtained in some cases.